Portable devices often contain components requiring electrical power and in some cases the required electrical power can have relatively high voltage and current ratings. Receptacles have been designed to provide power to such portable devices. Often, receptacles are designed with mechanical interlocking features to ensure that a connector from the device is properly inserted into the receptacle. However, as described further below, such mechanical interlocking features do not typically provide electrical testing features.
Refrigerated shipping containers are one example of a portable device that requires power. Refrigerated shipping containers are used to ship goods throughout the world. Such refrigerated shipping containers can be transported on trains, trucks and ships and the containers are often stationed at ports, warehouses, and distribution centers. While the refrigerated containers are located in these various modes of transportation and storage, they often need electrical power to operate the refrigeration unit of the container. The refrigeration units in refrigerated shipping containers typically operate at relatively high voltage and current ratings. For example, many refrigerated shipping containers operate at 480 volts AC and 32 amps. Electricity is delivered to refrigerated shipping containers via receptacles that can be found, for example, in ports and distribution centers and on ships, trains, and trucks.
As shown in FIG. 1, an example refrigerated shipping container 105 can include a refrigeration unit 110 with a power cord 115 and a connector 120. The connector 120 can have a variety of configurations. In the example shown in FIG. 1, the connector 120 is a pin-and-sleeve type of connector with four pins. The connector 120 of refrigerated shipping container 105 can connect to a socket comprising a receptacle such as the reefer receptacle 125 shown in FIG. 1. In some instances, the socket can be an interlocking socket. Interlocking sockets provide added safety in that they require a secure mechanical connection between the receptacle and the connector before the receptacle is energized and power is delivered to the connector 120. Examples of interlocking sockets are described further, for example, in U.S. Pat. Nos. 4,604,505, 8,475,192, and U.S. Patent Application Publication No. 20130001052.
While existing interlocking sockets, such as the one comprising reefer receptacle 125 shown in FIG. 1, provide a mechanical interlock with the connector, they do not provide any information regarding the safety of the electrical connection beyond the receptacle, including the connector or any conductors or electrical equipment downstream of the connector. For example, because the connector and power cord remain attached to the refrigerated shipping container while it is transported and stored, it is common for the connector and/or the power cord to become damaged. As illustrated further in FIG. 2C, damage to the connector and/or the power cord can produce an unsafe condition, such as a bolted fault or ground fault, when a damaged connector 220 is connected to a receptacle and energized. Unsafe electrical conditions can also arise downstream of the power cord at the compressor or other electrical components of the refrigeration system. Such unsafe conditions can be exacerbated in situations where refrigerated shipping containers are stored in racks closer to the main incoming electrical source where a higher short circuit current exists. As illustrated in FIGS. 2A and 2B, some ports and shipping areas are transitioning from horizontal reefer runways 205 shown in FIG. 2A, where reefers are placed adjacent to each other on the ground, to reefer racks 210 shown in FIG. 2B, where reefers are stacked vertically in a more dense arrangement that is closer to the incoming power source. The more dense arrangements involving reefer racks can increase the possibility of unsafe electrical conditions that could produce arcing.
Accordingly, there is a need for an improved receptacle that can alert users to unsafe electrical conditions in the connector, power cord, or electrical components downstream of the connector and power cord towards and including the load. There is a further need for an improved receptacle that prevents the receptacle from being energized when an unsafe electrical condition is detected.
While the solution described in the following text and the attached figures largely focuses on examples of improved receptacles for use with refrigerated shipping containers, those in the field will recognize that the improved receptacles can be used in other applications. The improved receptacles described herein can be useful in providing electrical power to any device. Furthermore, the embodiments described herein can be applied to other electrical devices including switches and indicators.